1. Technical Field of the Invention
The present invention relates to a method of generating a path to accelerate the movement velocity of a multiaxial robot and relates to a control apparatus for the multiaxial robot.
2. Related Art
Recently, in the field site such as of a productive facility, great variety of industrial robots is used. Such industrial robots include so-called multiaxial robots having a plurality of joints (axes). Such multiaxial robots are used for the works of welding, coating, parts assembly, parts conveyance, and the like. Such a multiaxial robot, by the nature of the role played by it, is required to reduce its time duration from a start point to an end point, i.e. required to increase movement velocity.
Methods of controlling the acceleration/deceleration of the movement of a multiaxial robot for increasing movement velocity are well known. For example, according to one of such methods, a basic movement velocity pattern is formed into a trapezoidal shape to calculate a maximum acceleration according to the posture of the robot, followed by correction of the velocity pattern. According to another method, a multiaxial robot is moved under bang-bang control using a maximum torque pattern which is based on a maximal principle.
In this trapezoidal velocity pattern, acceleration is constant in the time duration that corresponds to each of the shoulder portions. However, since the actual posture of the multiaxial robot changes moment by moment, the maximum acceleration changes in a non-linear manner. In other words, although a maximum acceleration can originally be achieved in a non-linear manner, the acceleration in the above movement velocity pattern is performed in a linear manner. Therefore, the motors are not able to sufficiently exert their performances. Regarding the latter method, although there are actually constraints imposed by the upper limit of the movement velocity (constraint conditions), such constraint conditions are ignored. As prior art related to the control of acceleration/deceleration mentioned above, control methods disclosed in patent documents JP-A-2000-094371, JP-A-2002-132349 and JP-A-2002-321178 are well known.
The outlines and problems of the control methods disclosed in the patent documents set forth above are explained below.
The patent document JP-A-2000-094371 discloses a control method in which the acceleration in the trapezoidal velocity pattern is changed according to the weight of a work and the inertia. However, according to this control, the acceleration is increased at a constant rate based on the acceleration calculated at the time of attaching/detaching the work. Accordingly, the acceleration cannot go beyond the limitation imposed by the attributes of the trapezoidal velocity pattern.
The control method disclosed in the patent document JP-A-2002-132349 also mentions about the time duration of performing acceleration/deceleration based on a trapezoidal velocity pattern. Specifically, in the time duration, an actual acceleration curve is adjusted so as to be in conformity, as much as possible, with a preset limiting acceleration curve to enable output of larger acceleration.
However, it is unclear in this patent document how the preset limiting acceleration curve is calculated. Further, the curve is provided, as a parameter, for each of the axes, each of the movement directions and each of accelerations/decelerations. Accordingly, in this control method: (1) a plurality of parameters are provided and thus the management is troublesome; in addition, (2) the parameters, which are discrete values, cannot precisely be in conformity with the acceleration curve; further, (3) although a maximum acceleration depends on the posture of the robot, no consideration is given to this point. Therefore, this control method is not regarded to be a generic method.
The patent document JP-A-2002-321178 discloses a control method in which a dynamic equation is solved taking account of the motion dynamics of each of the axes of a robot at the start point of a movement, the end point of acceleration, the start point of deceleration, and the end point of the movement to thereby minimize the acceleration time and the deceleration time. However, with this control method, acceleration/deceleration cannot be minimized at action points other than the action points mentioned above.